Yet another of my many requests tht no one else seems to have the answer too (or any interest it).

Anyway, nevermind, because I figured it out. The problem was the files take a bit of time to stream onto the N900, so by slowing down the slideshow to about 10 or 12 seconds per picture, that takes care of the lag and the ensuing lock-up/crash.

As well, there is no need to reencode, a la FUPPES server or Knots' abilities. Just allowing the little bit more time for the pics to arrive makes everything run smoothly.

One minor annoyance - Media Box defaults its slideshow to 3 seconds and resets it every time - there is no way to set and save at a different time interval, that I can find.